roof pitch for snow

How Does Roof Pitch Affect Snow Load?

Winter is in full swing here in Colorado, and you know what that means: snow! …and lots of it.

With a lot of snow comes beautiful landscapes and great opportunities to get outside and have some fun. However, heavy snowfall also brings with it the potential to damage roofs, as accumulated snow can create a burden for roofs that are not designed to withstand it. This burden can cause water leaks which, in turn, can result in costly mold, rot, and deterioration of structural supports.

Additionally, heavy snow load can pose a significant threat to the safety of those below a roof, especially when roof heights are higher and temperature swings happen. For these reasons, it helps to understand how roof design plays a role in mitigating the risks posed by heavy snow loads.

Designing Roofs for Effective Snow Shedding

A key factor in the design of any roof is its pitch, also referred to as roof ‘slope’. In layman’s terms, roof pitch is just a measure of how steep a roof surface is.

In the roofing industry, roof pitch is typically measured in inches of rise over a one-foot length of roof. For example, if a roof’s angle rises four inches every foot, its pitch is commonly denoted as ‘4/12’. Steeper roofs will naturally have higher numerators, here. A good example of the highest-pitched roof found in Colorado is that of an Alpine Chalet-style home, which can have a roof with a pitch of 20/12 in some cases.

Now, let’s explore the relationship between roof pitch and snow load.

Higher Pitch = Faster Snow Creep

Generally speaking, low-slope roofs will naturally retain more snow than steeper roofs. However, you don’t necessarily need a steep roof for gravity to bring accumulated snow to the edges of the roof. In fact, the Federal Emergency Management Agency (FEMA) has found that roofs with angles as low as 10 degrees can be effective at shedding snow.

snow load roof pitch

It stands to reason that a steeper roof is going to do a better job at shedding snow. And, the faster snow naturally falls off the roof, the less time it will have to build up and create a potential problem.

In this way, higher roof pitch can be directly correlated to overall snow shedding efficiency of any given roof in Colorado.

Contributors to Rooftop Snow Accumulation

A roof with an especially steep roof pitch can still develop dangerous snow loads. That’s because virtually all roofs have valleys, inclusions, or structural obstructions that will disrupt snow shedding.

Some of these contributors to rooftop snow accumulation include:

  • Roof parapets
  • Valleys in saw-tooth roofs
  • Vents, stovepipes, or skylights
  • Chimneys
  • Dormer windows
  • Solar panels

Also, because wind direction and speed can play a significant role in the accumulation of snow on a roof, it’s often difficult to predict exactly where and when snow might build up.

So, what can be done to make it easier for snow to fall from a roof, thus reducing the likelihood of snow loading?

As it turns out, not much. With a heavy enough snowfall, nothing can be done to altogether eliminate the chance of snow building up on a roof. However, some roofing materials do a better job at shedding snow than others. These include metal roofs and single-ply membrane roofs.

But, not every home or business is a candidate for metal roofs or single-ply membrane roofs. So, it’s safe to say that Colorado snow loads on rooftops cannot be 100% prevented. Rather, they can only be managed.

One way to do this is to install snow guards or snow cleats along the edges of a roof. These staggered obstacles can help prevent snow from suddenly sloughing off roof sides. The idea is to give accumulated snow a chance to collect intentionally along roof edges, where it will naturally melt over time.

Snow cleats are also seen as a safety feature that protects the people and property below.

Another common strategy for managing snow loads is to properly insulate the roof. A well-insulated roof won’t radiate as much heat, and the result is less formation of ‘ice dams’ which can pose a serious problem down the line.

Is Your Roof Ready for the Coming Snow? 

At A-to-Z Roofing & Exteriors, all we do is protect Colorado homes and businesses from the elements.

If your roof needs some attention in preparation for the snowy months to come, contact us. We’ll be happy to provide a thorough roof inspection and advise you on the steps you can take to help keep your home or business safe this winter.

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